Diagnostic systems designed for ease of use and/or low cost may be desirable for field applications. For example, screening for low hemoglobin concentration, or anemia, is critical in antenatal care, as untreated anemia in pregnancy can lead to pre-term delivery, low birth weights, and increased risk of maternal and fetal deaths. Because the risk factors for anemia include pregnancy, micronutrient deficiencies, and infectious diseases, anemia is especially prevalent in pregnant women in developing countries. Existing methodologies for hemoglobin determination range from conductometric to microcytometery. In addition to measuring hemoglobin concentration, it is important for pregnant women to be screened for HIV infection. If diagnosed in a timely manner, both anemia and HIV can be effectively treated (e.g., with iron supplements and anti-retroviral drugs, respectively), allowing for dramatic improvements in outcomes for both mother and infant. The disclosed subject matter addresses the needs of this and other applications.